1. Field of Invention
The present invention related to filters and placement of filters in a light engine. The present invention relates to the provision of a neutral dark state in an imaging device. The present invention is more particularly related to the production of a neutral dark state in a Liquid Crystal on Silicon (LCOS) based video projector.
2. Discussion of Background
The components of an LCOS based video projector 100 are explained by example of a light engine with reference to FIG. 1. As shown, white light 110 is generated by a light source 105. The light is collected, homogenized, polarized, and formed into the proper shape and otherwise processed by optics (not all shown for clarity). The light then enters a prism assembly 150 where it is broken into red, green and blue polarized light beams. A set of reflective microdisplays 152A, 152B, and 152C are provided and positioned to correspond to each of the polarized light beams (the prism assembly 150 with the attached microdisplays is called a kernel). The beams then follow different paths within the prism assembly 150 such that each beam is directed to a specific reflective microdisplay. The microdisplay that interacts with (reflects) the green beam modulates the green content of a full color video image. Similarly, the red and blue contents of the full color image are modulated by corresponding “red” and “blue” microdisplays. The prism assembly 150 then recombines the modulated beams into a modulated white light beam 160 that contains the full color video image. The resultant modulated white light beam 160 then exits the prism assembly 150 and enters a projection lens 165. Finally, the image-containing beam (white light beam 160 has been modulated and now contains the full color image) is projected onto a screen 170.
The black state of the video projector 100 is produced, for example, when the microdisplays are not energized. That is, light rays reflected from each of the microdisplays are not intended to be modulated or form part of the projected, making a black screen. Dark, but not 100% black, scenes in pictures or videos displayed on the screen 170 will likely have varying amounts or portions of a scene that are intended to be black.